Longnecker
et al. demonstrate a powerful association between DDE levels
in mothers' serum and the likelihood of premature birth. The higher
the contamination level, the more likely was preterm birth. They also
show that contamination is linked to the baby's size, with babies more
likely to be small for their gestational age when born to mothers with
higher DDE levels.

"
strongly suggest that DDT use increases preterm births, which is a
major contributor to infant mortality. If
this association is causal, it should be included in any assessment
of the costs and benefits of vector control with DDT."

Interviewed
by the British science magazine, New
Scientist, Dr. Matthew Longnecker (US National Institute of Environmental
Health Sciences), the lead author of the report, estimated that DDT use
in the United States could have been responsible for as much as 15%
of infant deaths during the 1960s.

What
did they do?
Longnecker et al. analyzed data and samples from a prospective
study conducted of the causes of neurological disorders and other conditions
in children born to mothers pregnant in the US between 1959 and 1966 (Niswander
and Gordon 1972). The data were compiled in the US Collaborative Perinatal
Project (CPP) , which enrolled some 42,000 women over that time span and
evaluated 55,000 babies. Of the total sample of women participating, the
vast majority deposited sufficient serum into a bank to allow subsequent
measurement of DDE levels. Details of the sampling are available in the
paper.

Longnecker
et al. measured concentrations of p,p'-DDT and p,p'-DDE
in serum samples taken from the pregnant mothers. They then evaluated
the DDE concentrations in relation to the chances of a pre-term birth
and infant size (controlling for gestational age).

What
did they find?

The
likelihood of preterm birth increased steadily with increasing concentration
of DDE in the mother's serum
(p < 0.0001).

The
likelihood of the baby being small for its age was highest for babies
whose mother had the highest DDE concentration). Similarly, the chances
of a baby weighing less than 2500 grams (or 5 pounds, 8 ounces) increased
dramatically with increasing DDE concentration. The highest levels of
DDE increased that likelihood by over four-fold. (p < 0.0001).

The
authors were able to detect the onset of these DDE impacts at a concentration
of 10 micrograms/liter.

What
does this mean?

DDE
blood levels in the US are now well beneath those concentrations detected
in this study (made of blood samples obtained in 1959-1966) and beneath
the apparent threshold for the effect detected in the authors' statistical
analysis (10 micrograms/liter). Hence even though DDE contamination persists
in people in the US, similar studies today in the US would be unlikely
to detect an effect. This is not the case, however, in countries where
DDT continues to be used for insect control.

According
to the authors:

"In
tropical countries, where DDT is used for malaria control, blood concentrations
of DDE can greatly exceed the range observed" in the sample they
studied. If DDE causes premature birth, it is likely to cause increased
infant mortality.

They
go on to observe that "Benefits of vector control with DDT might
need to be reassessed in the context of this adverse effect on human beings
and the availability of alternative methods of vector management."
This is a cautious way of stating that DDT's potential contribution to
infant mortality should be factored into decisions about phasing out DDT
use, increasing the urgency of finding safe and affordable alternatives.